In general, as outdoor light emitting devices, electric billboards using a neon lamp, a CCL (Cold Cathode Lamp), and LEDs (Light Emitting Diode) are widely used. As indoor light emitting devices, an EEFL (External Electrode Fluorescent Lamp), a CCFL (Cold Cathode Fluorescent Lamp), and light emitting diode electric billboard are used.
The neon lamp or the CCL consumes a large amount power because it uses high-voltage power, so a danger of an electric shock or a fire is high and the lifespan is short. Further, the EEFL or the CCFL is difficult to use outdoor because it uses a high frequency, the intensity of illumination is low and the lifespan is short.
Further, in an electric billboard using LEDs, the rear side of a light emitting side is blocked by a cover because the wires on the rear side are finished with a black sheathing, so light is emitted only in one direction.
Recently, light emitting devices are used not only for lighting, but for advertising, so they are manufactured in various aesthetic deigns and used for interior decoration.
However, there is a limit in esthetic designs of the light emitting devices due to the limit in the size of lamps and the size of stands supporting the light emitting device.
Accordingly, a plurality of light emitting elements is attached to a transparent electrode to an aesthetic design and they are controlled to show characters or symbols through the transparent electrode. Further, there are even transparent electric billboards that can show moving images. Those transparent electric billboards are mounted with a plurality of light emitting elements having two electrodes, three electrodes, or four electrodes on a transparent electrode. A transparent electric billboard has been disclosed in Korean Patent No. 79950 (Nov. 21, 2007).
However, the transparent electric bulletin board as manufactured for aesthetic interior decoration or advertisement does not have an insulating function that can maintain the interior temperature of a building. Accordingly, when it is installed around windows of a house or an office building, it is expensive to heat and cool the building.